MONTREAL (AFP) – Health officials in Canada have identified a case of swine flu that has proved resistant to the antiviral drug Tamiflu, media reports said Wednesday.

The case was detected in a Quebec man in his 60s, who had been taking a smaller-than-recommended dose of the drug before coming in contact with his son, who was ill with the virus, The Journal de Quebec and other local newspapers reported.

The elderly patient, who also suffers from chronic bronchitis, presumably already had become infected with the A(H1N1) virus while taking the Tamiflu medication — which any rate was administered in doses too small to ward off the virus.

Doctors called the revelation “disquieting” proof of the virus’s ability to evolve quickly, and noted a handful of similar drug-resistant swine flu cases that have cropped up elsewhere.

“This would be the first case to our knowledge of Tamiflu resistance in swine fly in North America,” said Guy Boivin, a physician at the Laval University Medical Center in Quebec, noting cases of drug resistance in Denmark, Japan and Hong Kong.